The standing crop and succession of marine microalgae are described for blooms in the surface water of a tide crack in the permanent ice of the Ross Ice Shelf at White Island, McMurdo Sound, Antarctica. The dominant microalgae during late November were Chlorophyta (Pyramimonassp.). Bacillariophyceae (diatoms) were dominant from early December until the end of the study in late January. Five species were most abundant:Nitzschia cylindrus, Nitzschia curta, Nitzschia obli‐quecostata, Fragilariasp., andSynedra tabulata. The concentration of chlorophyllawas at the highest level (30.0 μgl‐1) whenPyramimonassp. were most abundant. Incident light and the percentage transmission of light to a depth of 1 m in the tide crack were also at maximum levels at this time. The chlorophyllaconcentration decreased to below the limits of detection after the thaw in mid‐January when there was an abrupt increase in the temperature and a decrease in the salinity of the surface waters in the tide crack. The concentration of dissolved oxygen was at a maximum when the diatoms were most abundant.